Reimers Research Topics

Research in the Reimers Group is focused around the simulation and modelling of the properties of molecules in excited states, including the interactions of these molecules with solvents, proteins, and electrodes. This involves the development of quantum-mechanical methods for studying coupled electronic and nuclear motions, the application and development of ab initio, density-functional, and semi-empirical techniques for computing molecular electronic structure, and the development of mathematical modes to describe newly developing innovative experimental techniques. In recent years, the research profile has been expanded to include experimental Scanning-Tunnelling Microscopy (STM), a technique that allows a current to be passed through individual molecules assembled on a surface, and the theoretical interpretation of the experimental results.

Molecular electronics and Nanotechnology

Molecular Electronics is one of the fastest growing research fields. It is the ultimate in nanotechnology, being described as “the breakthrough of the year” in 2001 by Scientific American magazine. In principle, it offers a means by which electronic devices can be produced on much smaller length scales than is feasible with silicon-based technology, attaining, for example, over a thousand-fold increase in the capacity of the memory sticks and DVD’s currently used for portable mass data storage. Fundamental research in this area conducted by the Reimers group ranges from mathematical and computational modelling of intermolecular and intermolecular charge and energy transport to the development of robust, predictive computational methods for steady-state conductivity through single molecules to the measurement and interpretation of STM images. Applied research in this area is performed under the auspices of The University of Sydney Molecular Electronics Group, combining these expertise with the 50-year experience of Em. Professor Noel Hush in electron-transfer theory, the 25-year experience of Professor Maxwell Crossley in the targeted synthesis of molecules for Molecular Electronics, and the microscopy expertise of Dr. Pall Thordarson.

Molecular Memory design and construction is currently a major project of The University of Sydney Molecular Electronics Group. This work is funded jointly by the Australian research Council and Intel.

Photosynthesis and Solar-Energy

Photosynthesis, the conversion of solar to chemical energy by plants and bacteria is central to most forms of life on this planet. The first chemical step of this process is primary charge separation in which solar energy is converted to electrical energy for temporary storage within the organism. Fundamental research in the Reimers group concerns understanding the structure and function of the photosynthetic reaction-centre proteins in which the solar energy is harvested, converted to electrical energy, and then converted to chemical energy. These proteins are extremely complex molecular-electronic devices operating on the nanoscale at up to picosecond rates. Intrinsically they are quantum devices involving close coupling of electronic and nuclear motions in order to operate, being controlled by long-range electrostatic interactions from the protein that are readily modulated experimentally by molecular biologists using site-directed mutagenesis.

Photovoltaic Design research conducted by the Reimers group concentrates on the biomimetic application of the principles learnt from studying photosynthesis to the design and construction of artificial devices for commercial electrical energy production. All research is conducted under the auspices of The University of Sydney Molecular Electronics Group in association with Dr Paul Dastoor at The University of Newcastle. Fundamental research includes developing an understanding for the basic principles through which current polymer-based solar cells operate. Applied research is directed towards the development of a new paradigm in solar electricity production: a device that mimics all the stages of photosynthesis up to the storage of the separated electrical charges, attaching these stores to external electrodes. This is a fundamentally different technology to the inorganic silicon-based photovoltaics that dominate current commercial markets, the near-commercial alternate semiconductor Gratzel-type electrochemical solar cell technology, and the developing polymer-based molecular device technology.

Chemical Spectroscopy and Solvation

Spectroscopy often provides high resolution data concerning the precise nature of the electronic and vibrational motions of small molecules. Interpretation of this data is often a complex task, however, and in the Reimers group this is aided through state of the art calculations using ab initio methods such as CASPT2, EOM-CCSD, and SAC-CI as well as using modern density-functional approaches. This work also enables computational techniques for application to complex biological or nanotechnological device problems to be standardized and calibrated. Typical applications range from small aromatic molecules such as benzene, pyridine, and the azines to inorganic charge complexes such as the bis-ruthenium Creutz-Taube ion.

Solvation processes significantly modify molecular spectroscopy, particularly when ions are involved and when hydrogen-bonds form to the chromophores. A great deal of information is known experimentally about these processes, though much is yet to be interpreted. A long-term project in the Reimers group is the understanding of the nature of hydrogen bonding to molecules in molecular excited states. The absorption of light in biological systems can result in hydrogen-bonded molecules becoming electronically excited, a process that could threaten the structural integrity of the system. We have isolated several novel paradigms for hydrogen bonding that occur onto molecules in excited states.

Density-Functional Theory Development

Computational approaches to the understanding of electronic properties of large systems, such as conductivity between electrodes through a single molecule and conjugated polymers, usually involve the application of DFT rather than ab initio approaches due to its computational efficiency. While this method is very suited to most applications in chemistry, we have demonstrated that it has a variety of systematic failures all of which are pertinent to these technological applications. Work in the Reimers group focuses on the identification of these weaknesses, the development of computational strategies optimized to avoid them, and the development of new and improved DFT approaches.

Electronic-Structure computational methods in common use

Ab initio

Gaussian-03, MOLCAS, MOLPRO, ACES-II, Turbomole

DFT- molecular focused

ADF

DFT – solid-state and liquid-state focused

VASP, SIESTA, CP-MD

Semiempirical

INDO-MRCI (our own code), MOPAC, SCC-DFTB

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